System and method for reinforcing structures

Abstract

Cost-effective reinforcement system for frames walls helps support against failure from violent lateral forces. Strips of resin-impregnated textile in crossed pairs are attached to frame members. Attachment of ends of strips is ductile due to use of multiple fiber anchors.

Description

FIELD OF THE INVENTION

The present invention relates to building methods, and more particularly to a method of reinforcing structures against lateral forces that is well suited to retrofit of existing wood-framed buildings.

BACKGROUND OF THE INVENTION

Many modern buildings, including most residences, are supported by a framework consisting of an array of vertical support members connected at top and bottom by horizontal connecting members. The most familiar example of this type of construction in the United States is the wooden frame house with 2×4 wooden studs connected by a wooden bottom plate at the bottom and a wooden top plate at the top.

The bottom plate connects the frame to the foundation and the top plate connects to the roof. The studs are typically attached to the top and bottom plates by stiff attachment means such as nails or screws. The wooden framework provides the compressive strength sufficient to support the weight of the walls and roof. However, a conventional wooden framework does not have much resistance to the lateral forces that may result from earthquake or high wind.

Typically, a degree of shear bracing is added in the form of some diagonal “let-in” braces added between vertical studs. The braces are to prevent twisting of the framed structure, such as could be caused by warping of the studs or plates as the wood reacts to varying temperature and humidity conditions. Horizontal blocking members are attached between studs for various reasons, such as to increase the stiffness of a wall where cabinets will be attached or to maintain lengthy studs parallel to each other.

The sheathing of the walls, such as plywood or gypsum board attached over the framework, adds to the resistance to lateral forces. Modern experience in major earthquakes and more sophisticated modeling and testing techniques have shown that, in the past, the role of wall sheathing in providing shear strength may have been over-estimated. In many regions throughout the world, building codes have been made stricter and new buildings are more resistant to lateral forces.

It is well known that a framed wall does not typically have good resistance to forces normal to the plane defined by the wall. Frequently, especially in older structures, a framed wall is supported against normal forces mainly by the attachment of other walls. Structures that have experienced strong lateral forces, such as from earthquake or wind, are often flattened except for corners where multiple walls joined. Persons warned of high wind, such as from a hurricane, may take advantage of this effect by sheltering in an interior corner of a building. However, other disasters such as a tornado or earthquake may not allow time for a person to find the strongest location within a structure.

Unfortunately, a great many framed structures that were built in compliance with less stringent codes are still in use and are not expected to be replaced for many years. Such structures include single family houses, multiple family residences, office buildings, and public structures. Occupants of such structures are endangered during a disaster such as earthquake or tornado by walls being knocked over and the roof subsequently falling down into the structure.

There is a worldwide need for methods to retrofit such structures to withstand better the forces from earthquakes and high winds. In some cases, even a degree of resistance to explosive or other sudden forces is desired.

At one time, it was believed that the most effective way to reinforce a structure that was not strong enough was to increase the stiffness of the structure such as by thickening certain members, adding stronger attachment means at strategic points of the structure, or adding more diagonal bracing.

It has been found that a more effective strategy for reinforcing a structure is to increase its ductility. Ductile reinforcement allows a structure to deform and recover in response to unusual forces.

If ductile reinforcement is stressed beyond its capacity, it typically fails in a gradual manner, allowing minutes or even hours for evacuation of the reinforced structure. A stiff structure frequently fails suddenly and catastrophically, crushing or trapping occupants.

One type of connector for reinforcing a structure in a ductile manner is a fiber anchor, as disclosed in U.S. Pat. No. 7,207,149 of Fyfe, et al., issued Apr. 24, 2007. It has been used to connect many structural elements, such as to reinforce the connection among masonry blocks that make up a wall.

When designing a ductile reinforcement system for a structure, it would be expected that ductile connectors such as taught in the Fyfe, et al. patent should be utilized instead of more traditional rigid connecting means such as nails, screws, or metal brackets. Other ductile materials should also be considered to replace traditional bracing or thickening of support elements.

A method for retrofitting a structure that is in use would preferably be one that can be implemented with minimal disruption of the occupants. It is preferable that it not be necessary to partially dismantle or cut into the structure, and that the floor or adjacent grounds not need to be dug up. For example, cables have been used to tie structures laterally to the ground or other physical features. However, a cable support system typically requires the structure to be attached to vacant ground or another feature and may require excavation to install.

Further, a retrofit method is preferably quickly installed with a minimum of noise, dust, and other disturbance of the occupants or neighbors.

There is a need for wall reinforcing or a retrofit method that is relatively inexpensive and thrifty with materials. There is further a need for a method to strengthen even historical structures without spoiling the original aesthetic design of the structure.

There is a need for a method of reinforcing an existing or new structure to resist lateral forces in order to avoid injury or death of the occupants and persons adjacent the structure, as well as to minimize property damage and to allow normal routines to carry on after a disaster.

SUMMARY OF THE INVENTION

The present invention is a system for reinforcing structures against earthquake, wind, and other strong lateral forces. The system increases the ductility of the structure and strengthens the structure against sudden forces in several directions.

The reinforcement system is attached to existing members of a framed structure or may be incorporated into a structure being newly built. The reinforcement system of the present invention generally includes a plurality of pairs of strips with high tensile strength attached to junction points between vertical and horizontal framing members, with anchor plates reinforcing the attachment of strips to the junctions of framing members.

The strips with high tensile strength are lengths of resin-impregnated textile made of fibers or filaments of materials such as fiberglass, graphite carbon, nylon, polyaramid, or materials of similar tensile strength and ductility. The fibers may be all one material or a mixture of materials of slightly different strength or ductility.

The ends of the strips are connected to the anchor plates with a plurality of fiber anchors that spread forces and prevent tearing out of the strips. The fiber anchors are lengths of roving that pass through boreholes in the anchor plates and the framing members and are attached with adhesive. The adhered ends of the roving are splayed out to cover a larger area of the plate in order to spread applied forces and prevent tearing out of the anchors.

The strips are preferably used in pairs, with each pair roughly resembling the letter “X,” having each of the four ends of the X attached to a anchor plate that is in turn attached to a junction of a stud with a top or bottom plate.

The system is quickly applied to an existing wall and requires minimal disruption of the room itself. The materials used are relatively light in weight and do not require special machining or design. The components of the system are applied in an efficient manner that maximizes the reinforcement value of a minimal quantity of materials. The system requires little special equipment and training, thus is suited for use in most countries or regions.

The components of the reinforcement system are thin and do not unduly affect the appearance or design of the structure being reinforced. Because the reinforcing system can be completely covered by appropriate wall sheathing or finish, even historical structures retain their integrity.

The system of the present invention greatly increases the resistance of a building to earthquake forces. Use of the reinforcement system also includes the following benefits: increases the ductility of the structure, uses a minimal amount of relatively low-cost and lightweight materials, is appropriate for use in most regions of the world, can be quickly retrofitted in existing buildings with minimum disturbance of occupants and neighbors, and does not spoil the appearance or design of a existing structure.

The features and advantages of the invention will be readily understood when the detailed description thereof is read in conjunction with the drawings wherein like reference numerals refer to like parts throughout.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an environmental front elevation view of the reinforcement system of the present invention, attached to a conventional framed wall.

FIG. 2 is an enlargement of the upper right corner portion of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an environmental front elevation view of reinforcement system 10 of the present invention, attached to a conventional framed wall 100. Framed wall 100 consists generally of frame members 101 (shown in phantom) and wall sheathing 110 for covering frame members 101.

Frame members 101 typically include vertical support members 102, such as first vertical support member 103 and second vertical support member 104. First and second vertical support members 103,104 for a single family house are typically “studs” of soft wood that are nominally 2 inches by 4 inches cross-section and of any needed length, frequently 8 feet.

Support members 103,104 are parallel and spaced apart from one another. The maximum spacing is usually specified by relevant building code for the region and the type of structure. FIG. 1 indicates an additional support member 102 between first support member 103 and second support member 104.

Vertical support members 102 must have sufficient compressive strength, in array, to support the weight of the structure. However, vertical support members 102 do not necessarily have sufficient rigidity to support themselves perfectly upright and parallel against gravity or twisting forces that arise from fluctuating temperature and humidity conditions. To maintain vertical support members 102 in parallel relationship, horizontal connecting members 105, including top connecting member 106 and bottom connecting member 107, tie together the top ends and bottom ends of vertical support members 102.

Bottom connecting member 107 connects the bottom ends of vertical support members 102 and also connects them to foundation 120. Top connecting member 106 connects the tops of vertical support members 102 and also connects them to the roof and ceiling (not shown).

Vertical support members 102 and horizontal connecting members 105 are typically connected together where they abut with rigid attachment means, such as nails, screws, or metal brackets (not shown). Herein, a “junction 109” is meant to describe the portions of a vertical support member 102 and a horizontal connecting member 105 within a few inches of the area where the two members 102,105 abut.

Frame members 101 for one wall typically are rigidly joined so as to form a structural element that has good compressive strength and good flatness, but does not typically have good resistance to forces normal to the plane defined by the wall. Frequently, especially in older structures, a framed wall is supported against normal forces mainly by the attachment of other, non-parallel walls. The framed wall may not have sufficient integrity to remain upright when stressed by a large lateral force and the main section will frequently tear apart from the rigidly attached corners.

Reinforcement system 10 of the present invention increases the ductility of the framed wall and spreads forces throughout the framed wall. This allows the framed wall to retain integrity along its entire length when stressed laterally and to remain connected to adjacent walls, foundation 120, and roof.

Reinforcement system 10 includes a pair of elongate strips 11, of a material with good ductility and good tensile strength. A preferred material for strips 11 is resin-impregnated textile 12, also known as fiber-reinforced plastic (“FRP”). Resin-impregnated textile 12 is typically composed of a textile stock that is woven or knitted from filaments, fibers, or yarns of high-strength fiberglass, graphite, polyaramid. The textile stock is impregnated with a suitable hardening resin such as an epoxy or ester. Other suitable materials may, of course, be employed.

Each FRP strip 12 includes a first end 13, a second end 14, and a middle portion 15 between ends 13,14. Each FRP strip 12 further includes an inner face 17 that is attached to wall 100 and an exposed face 18, opposite inner face 17, and which faces away from wall 100.

FRP strips 12 are attached in pairs, forming an “X” upon a section of framed wall 100. FRP strips 12 may be attached over existing wall sheathing 110 or directly on bare framing members 101 in a structure being built or remodeled.

It has been found through experimentation that reinforcement system 10 is strongest if FRP strips 12 are attached such that the longitudinal axis of one strip 12 of a pair is at an angle of nominally 90° to the longitudinal axis of the other strip 12 of the pair. Thus, the horizontal width of the “X” should be about equal to the vertical distance from bottom connecting member 107 to top connecting member 106.

Because ends 13,14 of FRP strips 12 are attached over a junction 109, that is, to both a vertical support member 102 and a horizontal connecting member 105, the width of the “X” will actually be a multiple of the spacing of support members 102. For this reason, FRP strips 12 cannot always be at a 90° angle to each other, but care should be taken to set up reinforcement system 10 to come as close as possible to the preferred angle of 90°.

FRP strips 12 may be precut to a length determined to yield a “X” of appropriate dimensions, or FRP strips 12 may be cut as they are used from a length or roll of FRP material 12.

It is convenient to attach ends 13,14 to frame members 101 initially with some temporary means, such as staples. Then ends 13,14 are attached permanently by ductile attachment means 30, such as a plurality of fiber anchors 32.

Each end 13,14 is attached to both a vertical support member 102 and a horizontal connecting member 105. To accomplish this, end 13,14 is attached so as to generally cover junction 109 where a vertical support member 102 and a horizontal connecting member 105 abut.

For example, in FIG. 1, first end 13 of first strip 12a is attached to both first vertical support 103 and top connecting member 106. First end 13 partially covers junction 109 surrounding the area where first vertical support 103 and top connecting member 106 contact each other.

To create each fiber anchor 32, a borehole 34 is created, which passes through an end 13 or 14 of FRP strip 12 and into a frame member 101, underneath end 13 or 14. Precut FRP strips 12 may include pre-punched holes at appropriate locations in ends 13,14. In this case, an electric drill would be inserted into a punched hole and borehole 34 finished by drilling about an inch into the wood of frame member 101. Alternatively, borehole 34 may be drilled directly through end 13 or 14 and into frame member 101.

A length of roving 35 is inserted into borehole 34. Roving 35 is typically a hank of fibers or filaments loosely twisted together. The fibers are of a suitable material such as high-strength fiberglass, graphite, polyaramid, or nylon. Roving 35 may desirably include a mixture of fibers of different materials.

Roving 35 may be pre-cut into lengths or each piece of roving 35 may be cut as needed. Each length of roving 35 is inserted into borehole 34 such that one end of roving 35 is at or very close to the bottom of borehole 34 and the free end 37 of roving 35 protrudes from borehole 34, such as by 0.5 to 2 inches.

If the diameter of roving 35 is substantially less than the diameter of borehole 34, it may be desirable to fold roving 35 in half and insert the folded end into borehole 34. This is conveniently done by pressing the folded end of roving 35 into borehole 34 with a tool such as a screwdriver. In this case, obviously, roving 35 must be cut into lengths that are twice the depth of borehole 34 plus 0.5 to 2 inches.

Borehole 34 with the inserted roving 35 is then backfilled with a suitable backfill material 36 such as a hardening adhesive resin, which may be epoxy, silicone, acrylic, or other suitable material that has high cohesive strength and good adhesion to wood and roving 35. Backfill material 36, after hardening, anchors roving 35 into borehole 34

Roving 35 is inserted into borehole 34 such that free end 37 protrudes by a slight amount, such as 0.5 to 2 inches. After borehole 34 is backfilled, free end 37 is attached to a surface of framed wall 100, such as existing wall sheathing 110. Free end 37 is attached in a two-step process. First, free end 37 is splayed apart so that the individual fibers or filaments that compose roving 35 are spread over an area at least two or three times wider than the initial diameter of roving 35.

In the second step of attaching free end 37, the splayed out free end 37 is attached to outer face 18 of FRP strip 12 with an adhesive, such as a hardening adhesive resin. The preferable qualities of the adhesive for attaching free end 37 are similar to the preferable qualities of backfill material 36. Therefore, the same resin is typically used for both purposes.

A typical method for backfilling borehole 34 and attaching free end 37 is to first provide a syringe (not shown) filled with a suitable backfill material 36 and having a blunt needle tip with a length about the same as the depth of borehole 34. Next, free end 37 is splayed apart by working it in the hands. The tip of the syringe is used to press roving 35 into borehole 34, then backfill material 36 is expressed as the syringe is withdrawn, to fill borehole 34 with backfill material 36. Additional backfill material 36 is deposited over free end 37. Free end 37 and the adhesive covering it may then be flattened and spread over outer face 18 near borehole 34 with a suitable tool, such as a plastic putty knife (not shown).

The purpose of splaying apart and attaching free end 37 to outer face 18 is to spread the lateral forces that may be applied by a earthquake or other event, so that fiber anchor 32 does not pull or tear apart from borehole 34 or FRP strips 12.

Each fiber anchor 32 so created attaches end 13,14 to one of the underlying frame members, 102,105. Each end 13,14 is preferably attached with a plurality of fiber anchors 32. Fiber anchors 32 are disposed such that some anchors 32 attach a given end 13, 14 to vertical support member 102 and some anchors 32 attach the same end 13, 14 to the horizontal connecting member 105 near junction 109 where the two frame members 102,105 abut. Thus, the plurality of fiber anchors 32 ductilely attach each end 13 or 14 to both a vertical support member 102 and a horizontal connecting member 105, and indirectly reinforce the attachment of the two members 102,105 to each other.

Middle portion 15 of each FRP strip 12 is attached to wall sheathing 110 by adhesive means, such as the resin that impregnates FRP strip 12. This resin may be a partially cured (“gelled” or “B-staged”) resin that is supplied as a component of FRP strip 12, or liquid resin that is applied at the worksite, such as by dipping a strip 11 into a container of resin, or by rolling or brushing resin over strip 11 that has been attached to wall 100 by temporary means or with ductile attachment.

The most preferred manner of practicing the reinforcement system 10 of the present invention, as illustrated in the drawings, is to further attach an anchor plate 20 to each junction of vertical support member 102 and horizontal connecting member 105 to which first end 13 or second end 14 will be attached.

Referring especially now to FIG. 1, anchor plates 20 are generally square plates, such as of wood or plastic. For use in a single-family house, typical dimensions are 12 by 12 inches with a thickness of about 0.25 inch.

The purpose of anchor plates 20 is to spread out forces. Because each anchor plate 20 is connected to both a vertical support member 102 and a horizontal connecting member 105, each fiber anchor 32 is effectively connected to both members 102,105 as well. Anchor plate 20 helps stabilize fiber anchors 32 such that each fiber anchor 32 helps reinforce against forces from any direction. Anchor plate 20 also helps ensure that fiber anchor 32 will not pull out under especially violent forces.

To begin the method of the present invention, a first anchor plate 20a is attached to the junction of first vertical support 103 with top connecting member 106. Preferably, a section of wall sheathing 110, of the same dimensions as anchor plate 20, is cut out from the existing wall 100 so that anchor plate 20 will end up flush with the outer face of wall sheathing 110.

Known attachment means such as nails, screws, bracket, or adhesives are used to attach first anchor plate 20a to both frame members 101. Second anchor plate 20b is attached to top connecting member 106 and second vertical support 104 in a similar manner. Third anchor plate 20c is attached to both bottom connecting member 107 and first vertical support 103. Lastly, fourth anchor plate 20d is attached to both bottom connecting member 107 and second vertical support 104.

Next, the other steps discussed above are followed: temporary attachment of strips 12, creation of boreholes 34 that pierce strips 12, anchor plates 20, and end in a framing member 101, insertion of roving 35 into borehole 34, then splaying out free end 37 and adhering free end 37 to anchor plate 20.

After all reinforcements 10 have been installed, wall 100 may be finished decoratively as desired. Paint or other wall finish such as paper may be applied directly over reinforcement system 10, or reinforcement system 10 may be covered with decorative paneling.

The invention has been discussed herein as a reinforcement system for a wood framed wall having sheathing such as wood or gypsum board (drywall). The method of the invention may be practiced in a similar manner for structures of other materials and construction, including but not limited to lath and plaster, cement board, or metal I-beam construction.

Although particular embodiments of the invention have been illustrated and described, various changes may be made in the form, composition, construction, and arrangement of the parts herein without sacrificing any of its advantages. Therefore, it is to be understood that all matter herein is to be interpreted as illustrative and not in any limiting sense, and it is intended to cover in the appended claims such modifications as come within the true spirit and scope of the invention.

Claims

1. A system for reinforcing a framed structure, the structure including: framing members including: at least one pair of vertical support members in parallel spaced-apart relation, one horizontal top connecting member connecting the top portions of the vertical support members, and at least one horizontal bottom connecting member connecting the bottom portions of the vertical support members; said system including:

a pair of strips of resin-impregnated textile, each strip adapted to reach diagonally from a junction of a top connecting member with a support member to a junction of a bottom connecting member with a different support member; each of said pair of strips including: a first end attached to the junction of a top connecting member with a vertical support member; a second end attached to the junction of a bottom connecting member with a vertical support member; an inner face disposed toward the framing members of the structure; an exposed face disposed away from the framing members of the structure; and a middle portion between said first and second ends; and

ductile attachment means attaching each of said four ends to each said junction of a connecting member with a support member.

2. The system of claim 1, further including:

four anchor plates, each of said anchor plates attached between one said strip end and one junction of a connecting member with a support member; said ductile attachment means further attaching each said anchor plate with a respective strip end and junction.

3. The system of claim 1, said ends of strips attached to the framing members such that said middle portion of one said strip crosses said middle portion of the other said strip.

4. The system of claim 3, said pair of strips attached such that the longitudinal axis of one said strip is disposed at a angle in the range of 70-110 degrees to the longitudinal axis of the other said strip.

5. A method for reinforcing a framed structure that includes framing members, including a first vertical support member and a second vertical support member in parallel spaced-apart relation, one horizontal top connecting member connecting the top portions of the vertical support members, and at least one horizontal bottom connecting member connecting the bottom portions of the vertical support members; the method including the steps of:

affixing a first anchor plate to the junction of the first support member with the top connecting member;

affixing a second anchor plate to the junction of the second support member with the top connecting member;

affixing a third anchor plate to the junction of the first support member with the bottom connecting member;

affixing a fourth anchor plate to the junction of the second support member with the bottom connecting member;

providing a first strip of material having: a first end, a second end, and a middle portion therebetween and with a length approximating the distance between the first and fourth anchor plates;

attaching the first end of the first strip to the first anchor plate using ductile attachment means;

attaching the second end of the first strip to the fourth anchor plate using ductile attachment means;

providing a second strip of material having: a first end, a second end, and a middle portion therebetween and with a length approximating the distance between the second and third anchor plates;

attaching the first end of the second strip to the second anchor plate using ductile attachment means; and

attaching the second end of the second strip to the third anchor plate using ductile attachment means.

6. The method of claim 5 wherein the longitudinal axis of the first strip is disposed at an angle of 70-110 degrees to the longitudinal axis of the second strip after both strips are attached to the respective anchor plates.

7. The method of claim 5, wherein each step of attaching an end of a strip to an anchor plate comprises the step of creating a fiber anchor, further including the sub-steps of:

creating a borehole that passes through the end of the strip, through the anchor plate, and into a framing member;

inserting a length of roving through the end of the strip, through the anchor plate, and into the framing member such that a free end protrudes from the end of the strip;

backfilling the borehole with adhesive to capture the roving; and

attaching the free end of roving to the end of the strip with adhesive.

8. The method of claim 7, wherein each step of attaching an end of a strip to an anchor plate comprises the step of creating a plurality of fiber anchors by repeating the sub-steps of claims 7 a plurality of times.

9. A method for reinforcing a framed structure that includes framing members, including a first vertical support member and a second vertical support member in parallel spaced-apart relation, one horizontal top connecting member connecting the top portions of the vertical support members, and at least one horizontal bottom connecting member connecting the bottom portions of the vertical support members; the method including the steps of:

providing a first strip of material having: a first end, a second end, and a middle portion therebetween and with a length approximating the distance between the junction of the first support member with the top connecting member and the junction of the second support member with the bottom connecting member;

attaching the first end of the first strip to the junction of the first support member with the top connecting member using ductile attachment means;

attaching the second end of the first strip to the junction of the second support member with the bottom connecting member using ductile attachment means;

providing a second strip of material having: a first end, a second end, and a middle portion therebetween and with a length approximating the distance between the junction of the second support member with the top connecting member and the junction of the first support member with the top connecting member;

attaching the first end of the second strip to the junction of the second support member with the top connecting member using ductile attachment means; and

attaching the second end of the second strip to the junction of the first support member with the bottom connecting member using ductile attachment means such that the middle portion of the second strip overlies the middle portion of the first strip.

10. The method of claim 9, wherein the ends of the strips of material are attached to junctions of framing members such that the longitudinal axes of the attached first and second strips form an angle of 70 to 110 degrees.

11. The method of claim 9, wherein each step of attaching an end of a strip to a junction using ductile attachment means comprises the step of creating a fiber anchor, further including the sub-steps of:

creating a borehole that passes through the end of the strip and into a framing member;

inserting a length of roving through the end of the strip and into the framing member such that a free end protrudes from the end of the strip;

backfilling the borehole with adhesive to capture the roving; and

attaching the free end of roving to the end of the strip with adhesive.

12. The method of claim 11, wherein each step of attaching an end of a strip to a junction comprises the step of creating a plurality of fiber anchors by repeating the sub-steps of claims 11 a plurality of times.